An optoelectronic device, such as a laser diode or a photo diode, is generally enclosed in a transistor outline (TO) package, which provides a conductive housing for the optoelectronic device. A laser diode converts an electrical signal into an optical signal for transmission over a fiber optic cable, while a photo diode converts an optical signal into an electrical signal. In order for a laser diode to convert an electrical signal into an optical signal, the electrical signal must be sent through the TO package of the laser diode. Similarly, an electrical signal from a photo diode must be sent through the TO package of the photo diode to external electrical circuitry. For high frequency operation, it is important to control the impedance seen by the electrical signals that flow into and out of the TO package.
In prior art laser diode based transmitter assemblies, the impedance is controlled, if at all, using internal resistors. These internal resistors dissipate approximately two thirds of the heat dissipated inside the TO package. The resistors are, therefore, a major source of heat within the TO package, which adversely affects the operation of the laser diode within the TO package. Additionally, once the resistors are in place within the TO package, it is difficult to change the resistors. Finally, resistors suitable for use inside a TO package are more expensive than other types of resistors.